Method of manufacturing integral finned tubing



Dec. 21, 1943. PENNER 2,337,490

METHOD OF MANUFACTURING INTEGRAL FINNED TUBING F iled April 15, 1940INVENTOR.

EDWARD PENNER ATTORNEYS Patented Dec. 21,1943

UNlTED STATES PATENT OFFICE METHOD OF MANUFACTURING INTEGRAL FINNEDTUBING corporation of Michigan Application April 15, 1940, Serial No.329,819

5 Claims.

The invention relates to integral finned tubing of that type in whichthe metal forming the fins is displaced axially and radially from theouter portion of the tube blank. This operation is usually performed byplacing the tube blank on a mandrel and feeding it axially with respectto the fin-forming means, such for instance as longitudinal series ofrolls circumferentially spaced about the blank. Thus, the fins will beformed "".,l5hl'0llgh0llt the entire length of the blank and 1 becauseof the displacement of the metal, the wall thickness intermediate thefins is necessarily reduced. Such tubing may be used in the manufactureof heat exchange units where the ends of the fin tubes are connectedinto headers o as form a sealed joint. This necessitates stripping thefins from the end portions of the tube, leaving a wall thickness whichis reduced from that of the original blank. It has been found that thewall thickness required for making a proper joint with the header isgreater than that which is sufiicient for the finned portion of thetube, but where the fins are formed as above described, the wallthickness must necessarily be the same throughout the length of thetube. Thus, the weight of metal in the tubes must be considerablyincreased if the end portions are to be made of greater thickness.

It is the object of the instant invention to obtain a method of formingintegral finned tubes which will have greater wall thickness in certainportions of their length than in other portions. More particularly, itis an object toincrease the wall thickness of the unfinned portions ofthe Figure 5 is a diagrammatic cross section illustrating the manner offinishing the outer surface of the tube ends;

Figure 6 is a view similar to Figure 2, showing a modified construction;

Figure 7 is an elevation, illustrating one construction of finned tubeunit having an unfinned return-bent portion. v

In manufacturing the finned tubes by my improved method the tube blanksA, preferably formed of seamless drawn tubing of copper or similarmaterial, are first placed upon a mandrel B which has one ormoreportions thereof reduced in diameter. Thus, as shown in Figure 1,the central portion 3' of the mandrel fits the internal diameter of thetube A, while the end portions B and B -are somewhat smaller indiameter. C are the rolls between which the tube is axially fed, saidrolls being suitably fashioned to progressively displace the metal inthe outer portion of the cross section of the tube, so as to formradially projecting helical fins A. The radial inward pressure of therolls upon the outer surface of the tube is resisted by the portion B ofthe mandrel, so as to preclude any contraction in diameter of thisportion. On the other hand, the portions of the tube which extend overthe portions B and B? of the mandrel are not so sup-, ported, and as aconsequence these portions will be contracted in diameter by thepressure of the rolls, instead of having fins formed thereon. Ifdesired, the tube may be contracted over the small diameter portions ofthe mandrel in advance of the feeding of the same into engagement withthe rolls, and thi is preferably done on the forward end of the tubewhich first comes in contact with the rolls. Thus, as shown in Figure 1,the forward portion A has been contracted by means of dies (not shown)to fit the mandrel portion B A tapering. pilot D is then engaged withthe forward end of the mandrel, preferably by means of a threaded shankD' engaging a correspondingly threaded aperture. This pilot is of adiameter to just clear the rolls, the portion A of the tube beingslightly larger. Thus, when the tube is fed between the rolls the latterwill merely slightly indent the outer surface of the portion A but thefollowing portion A which is over the mandrel portion B will have thefins A formed thereon. The rear end portion A of the tube which is overthe mandrel portion B, will be contracted by the pressure of the rollsto conform to the mandrel with only a slight indenting of its outersurface. Thus, as shown in Figure 2, the central portion of the tube isfinned while the opposite end portions are portion A by the mandrelportion B, as shown in Figure 3. The mandrel may then be completelyremoved, after which the end portionsof the tube may, if desired, befurther expanded by a suitable tool, such as F shown in Figure 4.Finally, these end portions are externally finished toremove theindentations therefrom, this operation being performed by any suitabletool, such as diagrammatically shown in Figure 5, having a pilot Gfitting within the tube and one or more external cutters H. This willnot only smooth the outer surface but will also remove any slighteccentricity between the outer and inner surfaces, so as to form anannular wall of uniform thickness.

For certain uses it may be desirableto form a tube having one or moreunfinned portions intermediate finned portions thereof. This may beaccomplished by the use of amandrel, as shown in Figure 6, in whichportions I fitting the internal diameter of the tube are connected by aportion J which is of smaller diameter. Thetube and mandrel are then fedbetween the fin-forming rolls, as previously described-which will merelyf, veiopment, removing the mandrel from the tube,

expanding the unfinned end portion thereof, and externally finishingsaid end portion concentric with theinner surface thereof.

3. Ina method of forming integral finned tubing having one or morefinned portions of exactly contract the portion K which is over themandrel portion J, while forming fins on the portions K and K atopposite ends of the portion K. The portion K will'thus be of greaterwall thickness than the portions K and K with only a slightly indentedouter surface. When the mandrel is driven out of the tube, this portionK will be enlarged to its original diameter and its outer surface maythen be finished to remove the indentations. Such a construction isuseful in the forming of return-bent finned tubes, as illustrated at Lin Figure '7.

A finned tube of the construction above described when formed fromseamless drawn copper tubing, will'have a high rate of heat exchange,

due to the thermal conductivity of the material and the integral fins.At the same time, the unfinned portions may be of any desired wallthickness without the necessity of increasing the we] thickness of thefinned portions. When, as shown in Fig. 4, the unfinned portion of thetube is finally expanded to a diameter greater than that of the originaltubular blank, the thickness of the walls will becorrespondinglyreduced. However, this thickness may be maintained to be at least asgreat as that of the finned portion, thereby avoiding any weakenedportion. What I claim as my invention is: 1. The method of formingintegral finned tubing having one :or more unflnned portions ofgreater'wall thickness comprising, placing atubular blank upon a mandrelhaving portions thereof fitting and supporting the wall of the tube, andone or more otherportions of smaller diameter spaced from the tube wall,feeding the blank and mandrel as a unit axially and throughout theirlength in intersecting relation to external fin-developing means whichexerts radially inward pressure in excess of the resistance of saidtubing, whereby fins will be developed and the wall thicknessintermediate the same reduced in the portion of the tube supported bythe mandrel'while the portions unsupported by the mandrel will beradially contracted to avoid substantial fin development, removing themandrel from the tube, and expanding the contracted portions thereof.

2. The method of forming integral finned tubing having an unfinned endportion'oi' greater wall thickness comprising, placing a tubular blankupon a mandrel for fitting and supporting the wall oi the tube buthaving an end portion of smaller diameter,feeding said tube and mandreltogether as a unit axially throughout their length in intersectingrelation to external fin-developing means which exerts radially inwardpressure predetermined length intermediate unfin'ned portions, the stepsof placing the tubular blank on a mandrel having a portion correspondingin length to each portion of the tube to be finned, said portion beingof a diameter to fit within and support the wall of the tubular blank,said mandrel also having portions of smaller diameter forming shouldersat opposite ends of each larger portion, and feeding the blank andmandrel as a unit axially in intersecting relation to extemai findeveloping means which exerts radially inward pressure in excess of theresistance of said tubular blank, whereby said blank will be radiallycontracted about said shoulders in the unsupported portions thereof andappreciable fins will be developed only on the supported portion betweensaid shoulders.

.4. In a method of forming integral finned tubing having one or morefinned portions of exactly predetermined length intermediate unfinnedportions, the steps of placing the tubular blank on a mandrel having aportion corresponding in length to each portion of the tube to befinned, said portion being of a diameter to fit within and support v thewall of the tubular blank, said mandrel also having P rtions of smallerdiameter forming shoulders at opposite ends of each larger portion,contracting the leading end of the blank over the smaller diameter ofthe corresponding end of the mandrel, and feeding the blank and mandrelas a unit axially in intersecting relation toexternal fin developingmeans which exerts radially inward pressure in excess of the resistanceof said tubular blank, whereby said blank will be radially contractedabout said shoulders in the unsupported portions thereof and fins ofappreciable height will be developed only on the supported portionbetween said shoulders.

5. In a method of forming integral finned tubing having one or morefinned portions of exactly predetermined length intermediate unfinnedportions, the steps of placing the tubular blank on a mandrel having aportion corresponding in length to each portion of the tube to befinned, said portion being of a diameter to fit within and support thewall of the tubular blank, said mandrel also having portions of smallerdiameter forming shoulders at opposite ends of each larger portion,contracting the leading end of the blank over the smaller diameter ofthe corresponding end of the mandrel, securing said blank on saidmandrel by means abutting the leading end of the blank, and feeding theblank and mandrel as a unit axially in intersecting relation to extemaifin developing means which exerts radially inward pressure in excess ofthe resistance of said tubular blank, whereby said blank will beradially contracted about said shoulders in the unsupported portionsthereof and fins of appreciable height will be developed only on thesupported portion between said shoulders.

' nnwxan PENNER.

